The field of this invention is positioning controls for variable displacement, axial piston pumps.
U.S. Pat. Nos. 2,733,666 to Poulos, and 2,977,891 to Bishop, show use of pressurized fluids available at the back plate. In these patents the fluid is used in different ways and for different uses than the present invention discloses. In U.S. Pat. No. 2,733,666, the fluid is channeled from the back plate to the opposite end of the cylinder barrel to re-engage the barrel with the back plate when they become disengaged as described in column 1, lines 27-55. In these two patents, the back plate is called a valve plate. In U.S. Pat. No. 2,977,891, the fluid is used to act on a piston system which regulates clearance between back plate and rotor of a radial piston pump as described in column 1, lines 53-63; in the last seven lines of claim 20; and as shown in FIG. 13.
Applicants know of no prior art using pressurized fluid to serve as a hydraulic stop in a cam plate positioning actuator to prevent the actuator from hammering on the back plate. This hammering of metal on metal occurs when the actuator is close to its fully retracted position, which is when the pump is working close to full displacement. The hammering of the movable part of the actuator against the back plate causes noise, wear, and vibration but is usually of short duration, occurring just before and just after the actuator is fully retracted. While fully retracted, the movable part is forced against the back plate thus preventing hammering. The hammering is caused by the varying forces exerted on the cam plate by pump pistons. In many hydraulic systems the pump seldom reaches full displacement, and therefore the problem does not occur. There are also many systems where the hammering is of such short duration that it is not objectionable or in some cases, unnoticeable. There are systems, however, where the noise, wear, or vibration of this hammering is undesirable. It is to those systems that this invention is directed.